Manufacture of magnetic bodies



A. F. BANDUR MANUFACTURE OF MAGNETIC BODIES Filed July 15, 1938 May 13, 1941'.

M/VENTOR A. f. BA D UR W A TI'ORNH sras' r manpeacrnna or MAGNE'ITEC ponies,

Application July 15, 1938, Serial No. 219,339

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This invention relates to the manufacture of magnetic bodies, and more particularly to the manufacture of magnetic cores of the insulated dust type in which finely divided particles oi magnetic material are coated with insulation and compressed into form.

In the manufacture of insulated dust magnetic cores the magnetic metal or alloy is generally cast in an ingot and pulverized to the required fineness, after which the particles are annealed, coated with a combination insulation and binder and finally compressed into the required shape. In the usual pressing operation the coated particles are placed in an open die cavity and subjected therein to very high'pressure by means of a compacting member applied against the top surface of the particle mass.

An object of this invention is the provision of improved methods and apparatus for compressing or forming finely divided and insulated magnetic material into shaped bodies having desirable magnetic and electrical properties, such as high permeability and high insulation resistance.

In accordance with one embodiment of the invention an improved magnetic core is produced by subjecting insulated dust to a succession of compressing operations in which the insulated magnetic particles are placed in a die cavity, pre-formed at a predetermined pressure with a compressingmember having a concave surface in contact with the particles, and finally compressed with a fiat surfaced member at a relatively high pressure that is several times the pre-forming pressure.

The new process and apparatus are especially suitable for the production of cores from nickeliron magnetic alloys of the Permalloy type and for convenience the invention will be described in detail as applied to that material, in conjunction with the appended drawing, in which Fig. 1 is a perspective view of one type of insulated dust magnetic core to which the invention is adapted;

Fig. 2-is an elevation partly in section or an apparatus for compressing insulated magnetic dust into cores in accordance with certain features of the invention;

Fig. 3 is a fragmentary sectional view showing the apparatus of Fig. 2 at a subsequent stage of the process, and

- Fig. 4 is a. fragmentary sectional view of a core compressing apparatus at the final stage of the compressing process.

In the preparation of the magnetic dust particles, the ingredients are melted together in a furnace and poured into a mold to form an ingot.

To develop a fine grain structure in the material the hot ingot is passed successively through progressively reducing rolls, after which the rolled material is quenched in. water at a temperature below its malleability range. The resultant ingots are crushed and pulverized in a hammer mill and attrition mill, or similar apparatus, into particles or dust of the required fineness. The dust is annealed to relieve the stresses produced by the pulverizing action and the particles are then coated with a suitable insulation, such as the mixture of magnesium silicate, sodium silicate and magnesium hydroxide disclosed in applicants Patent 2,105,070.

The insulated dust is then ready for pressing into a core, such as the ring shaped structure l0 shown in Fig. 1, which has a flat top surface it and is used extensively in communication equipment.

The cores are conveniently formed in accord" ance with this disclosure on well known apparatus, such as the conventional forming press of Figs. 2, 3 and 4, which has a stationary bed l2 and a ram or piston l3 actuated oy-some suitable power means (not shown),

For the first operation in the formation of the cores, a measured quantity of the insulated dust id (Hg. 2) is placed in a ring shaped cavity id in a sectional die it positioned on the press bed. Mounted on the press ram and aligned with the die cavity is a ring shaped pro-forming member H with a concave bottom end surface it. When the ram is advanced, the concave end of the ring is compressed against the dust in the die cavity and the dust is thus compacted into a pre-form it having a convex top surface, as shown in Fig. 3.

The pro-forming member can be secured to the ram by any suitable means or can be placed manually in the die cavity on the dust and engaged by the descending ram, as preferred.

The pro-forming pressure, as well as the degree of concavity on the prev-forming member, are important elements of the process. The optimum pressure values are determined to a, large extent by the size of the magnetic particles, and the type of particle insulation employed. In preforming mesh permalloy dust coated with the insulation disclosed in appllcants patent listed above, pro-forming pressures ranging from 15,000 to 30,000 pounds per square inch were satisfactory. For pre-zlorming a core one-half inch wide, a one-half inch radius on the preforming member gave good results. Some, ad-

"2,-241,44 1" I I I resulting from the adoption offtheee exceed and enable a" corresponding -per-.

- .formance improvement in the ap-= the die cavity in the same manner as the preforming member is positioned. The final forming member or ring has a flat end 2| for engaging the pre-form in the die cavity and compressing the pie-form into the core as the ram. is advanced. The pressure required for the final forming depends upon the size of the core particles and the insulation employed and a pressure of 250,000 pounds per square inch is used for the type of core described specifically herein.

Cores pressed by this method have a higher particle insulation resistance at given permeabilities than cores made by the former methods in which the loose dust was placed in a die and compressed into form with a flat ended. member. Analyses of these former cores showed that in some cases the magnetic and electrical properties were not uniform throughout the core section. In these cases the core portion just adjacent to the surface engaged by the forming member had a relatively high permeability, which is influenced by particle spacing, and low particle insulation resistance as compared with values at other portions of the core structure; It appears that in the former method when the flat member descends against the loose dust in the die cavity,

a turbulent action is developed, due to the currents set up by entrapped air. This action tends to shift the loose particles before compacting member this factor is improved. When the concave member is introduced, the loose dust is initially disturbed by escaping air, as before. However, as the member advances, it initially engages the dust at the cavity walls and shifts a proper proportion of'the dust towards the center. The optimum particle arrangement established in this way is fixed during the pre-pressing so that the final pressure is applied uniformly and the insulation eflectiveness is uniform throughout the core section. The new cores consequently exhibit higher particle insulation resistance values than cores of the same permeability formed by prior methods and these increases reduce eddy current losses when the cores are incorporated in coils. The reductions in coll losses paratus.

Although a specific process and core have been presented herein, it will. be apparent that modiflcations of the disclosure can be applied advan tageously to the manufacture of various malnetic cores and it is to be understood that the invention is limited only by thescope of the appended claims. 1

What is claimed is:

1. A method of forming iinsulated magnetic particles into magnetic bodies which comprises the steps of placing the loose particles in a walled die cavity, forming the particles into a mass by advancing a member into the cavity, said member being provided with a concave end surface to move some of the loose particles away from the cavity wall as the member advances and before it compresses the particles and then form the particles into a mass having a convex surface, and finally compressing the mass into the magnetic body with a second advanced into the cavity and having a flat surface for engaging the mass member.

2. A method of forming insulated particles of magnetic material into magnetic cores which comprises placing the insulated particles in a ring-shaped die cavity, compressing the particles by mean of a ring-shaped forming member advanced into the cavity, said member having a concave end portion for initially engaging the particles to place them in a predetermined arrangement and then compress them into a body having a convex surface, and finally pressing said body into a core with a second forming member having a flat surface for engaging the body.

3. A method of forming insulated particles of magnetic material into a magnetic core having a flat surface comprising the steps of first compressing the particles in a'die cavity-to form a body having a convex surface by advancing a forming member into the cavity, said member having a concave end surface for engaging the particles, and then forming the body into the core by engaging the convex surface with a second forming member having a flat end surface and applying sufllcient pressure to the second forming member to flatten the convex surface.

4. A method of forming insulated particles of magnetic material intoa magnetic core comprising the steps of placing a mass of the insulated particles in a die cavity, compressing the particles at a pressure between 15,000 and 25,000 pounds per square inch by means of a forming member advanced into the cavity and having a concave end surfaceior engaging the particles to form the mass into a body having a convex surface, and then applying a pressure around 250,000 pounds per square inch on the convex surface of the body by means of a second member advanced into the cavity and having a flat portion to engage and flatten the convex surface.

- ADOLPH F. BANDUR.

CERTIFICATE OF CORRECTION.

Patent No. 2, zhiAIn. may 15, 19in ADOLPH F. BANDUR.

It is hereby certified'thet error eppear s in the printed specification of the above numbered patent requiring correction as follows: Page 2,- sec- 0nd column, line 26, claim 1, strike omit the word "member" and insert the same after "second", line 21+, same claim; and that the said. Letters Patent should be read with this correction therein thgt the same-may conform to the recordof the case in the Patent Office.

Signed and sealed this 15th day of July, A. D. 19in.

Henry Van Arsdale',

(Seal') Acting Commissioner of Patents. 

